Toughening Mechanism of TC21 Titanium Alloy Linear Friction Welded Joints

doi:10.3901/JME.2025.12.127

Abstract

Abstract: Linear friction welding (LFW) is an effective method for achieving high-quality joints in titanium alloys. However, the presence of equiaxed grains and spherical dispersoids in the weld zone leads to a substantial reduction in joint toughness, despite an improvement in strength and plasticity. The as welded joint toughness is 16.7±0.5 J/cm², which is only 27% of the TC21 base material toughness (62±1 J/cm²). Previous research has indicated that a staggered basket-weave microstructure significantly enhances joint toughness. Accordingly, this study systematically investigates the microstructural evolution of the weld zone under various annealing heat treatment conditions, with the goal of achieving the staggered basket-weave structure. The experimental results show that, among the four annealing conditions, dual low-temperature annealing effectively modulates the joint microstructure, resulting in a substantial increase in joint toughness from 27% of the base material to 81%. Post-tensile testing, fracture occurs in the base material near the joint, and the hardness distribution transitions from a saddle-shaped profile to a uniform stable state. The equiaxed grains and original grain boundaries in the joint weld area weaken, and the dispersed grains transform into a layered interlaced basket structure. The proportion of alpha phase increases from 35% to 82%, the proportion of small angle grain boundaries decreases from 64.2% to 38.8%, the proportion of dynamic recrystallization increases from 20.2% to 43.5%, and the Smith factor decreases from 64.6% to 34.3% in the range of 0.4-0.5. The above results indicate that the joint has shifted from cleavage fracture mode to ductile fracture mode, fundamentally revealing the inherent mechanism of high toughness of the joint and providing theoretical basis and technical support for the optimization of high-strength and toughness connection technology for titanium alloys.

Key words: TC21 titanium alloy, linear friction welding (LFW), double low-temperature annealing, microstructure and texture, toughness enhancement mechanism

CLC Number:

TG166

ZHAO Pengkang, HONG Zhenyu, ZHANG Min, XIAO Xudong, YUAN Qilong, TAO Jun, ANTUNES Elsa, MA Ningshu. Toughening Mechanism of TC21 Titanium Alloy Linear Friction Welded Joints[J]. Journal of Mechanical Engineering, 2025, 61(12): 127-140.

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